Antiparasitic efficacy of ivermectin in naturally parasitized sheep.

Sixteen sheep harboring naturally acquired parasitisms were allocated to 1 of 2 treatment groups: (i) sheep given ivermectin in an oral solution at the dosage rate of 200 micrograms/kg of body weight, and (ii) those given the vehicle at a dosage rate of 0.25 ml/kg. All animals were necropsied at 2 weeks after treatment. Parasites and percentages of parasitic reductions, as demonstrated in this trial, were: Dictyocaulus filaria (99.4%), Oestrus ovis first stage instars (100%), Trichuris ovis (98.9%), Strongyloides papillosus (99.8%), Nematodirus spathiger (100%), arrested 4th stage Nematodirus spp (96.2%), Trichostrongylus colubriformis (100%), T axei (100%), Oster tagia circumcincta (100%), Haemonchus contortus (100%), and arrested Haemonchus spp 4th stage larvae (99.9%). The sheep showed no adverse effects due to ivermectin or vehicle administration.